Gardening in Langley: Pruning reduced black knot on plum trees

Send them to Anne Marrison via It helps me if you can give me the name of your region or address.

Dear Anne,

I have a plum tree that’s infected with black knot. What do I do with them after I’ve pruned them? Online it says burn them, but that’s not appropriate in this weather. If I throw them in the compost bin, will it be made into compost and spread the disease?”

Serena Chan, Vancouver

Dear Serena,

When the weather’s dry, burning definitely won’t do. Nor will home composting. The online information would probably refer to burning within wood stoves in houses or outside in normally moist rural areas. In cities outside burning is generally illegal.

But there’s another safe option, Serena: digging a hole at least 12 inches (30 centimetres) deep and deeper if you can then burying the black knot branches which you’ve cut into small pieces so that they fit better.

Lawns are good places for this type of burial. Any soil that’s unlikely to be dug up will also do.

It’s best to sterilize your pruners in a small container of 10 per cent bleach as you work on your tree and also after you’ve prepared the infected branches for burying.

The temperatures in city-type green waste composting should definitely be high enough to sterilize diseased plant material.

But in rural areas where garbage needs to be taken by home-owners to a transfer station, the habit in past years was to simply place infected plant material in the garbage. Green waste bins are now available in most transfer stations.

If you prune for black knot every winter, you will gradually have less infection. But some is inevitable because spores from untreated neighbourhood infections will continue to blow in on the wind.

Black knot pruning is best done in fall when trees are dormant and leafless. Spores are not released until early spring.

Dear Anne,

What is the best time to take cuttings from my white hydrangea and plant them. Will it grow successfully in a big pot as opposed to planting in the ground?

Terry Wong, Burnaby

Dear Terry,

Hydrangea cuttings root very easily and will do so in a big pot or in an outside garden provided you keep the soil moist with careful and frequent watering. It will be best if the pot stands in shade or semi-shade.

But this isn’t a good time to take cuttings because it’s so hot and dry. Hydrangeas hate both situations.

It would be best to wait until the late fall when the weather should be cooler. It would be even better if natural rain begins falling sometimes. If not, start the cuttings anyway but be very careful to keep the soil moist and put the cutting pot in shade.

I wonder if your hydrangea is a mophead (big, round heads and not much over three feet (one metre) tall or a shrub type. Both will grow nicely in a big pot, but every few years they will need to be taken out and root-pruned and top-pruned so that they fit better when put back in the same pot.

If your chosen pot is large, your new hydrangea may be contented for several years. But eventually, you’ll notice the soil in the pot dries out frequently and the shrub doesn’t look as healthy. Then you’ll know it’s time for some therapeutic pruning.

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